Low frequency ultrasensitive magnetic sensors are required for magnetocardiography (1pT at 10Hz) applications. MgO based magnetic tunnel junctions with RA=100–150Ωμm2 and tunnel magnetic resistance=100% were patterned into rectangular pillars with side up to 50μm. Sensors were incorporated in 500nm thick Co94Zr3Nb4 flux guides. Sensor linearization was achieved through internal (Co66Cr16Pt18 pads) and external (3.5mT) longitudinal bias fields resulting in sensitivities of 720%∕mT. Noise levels of 97pT∕Hz0.5 at 10Hz, 51pT∕Hz0.5 at 30Hz, and 2pT∕Hz0.5 at 500kHz were measured in the linear region of the transfer curve.
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Chaves et al. (2007) studied this question.
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